The invention refers to a self-propelled road milling machine, especially a cold milling machine, as well as a method for positioning the machine frame parallel to the ground.
In such road milling machines, the machine frame is supported by a track assembly comprising wheels or caterpillar tracks connected to the machine frame through lifting columns, the lifting columns allowing to adjust the machine frame to a specific horizontal plane or in parallel to the ground or under a predetermined longitudinal and/or transversal inclination.
A milling roller for working a ground or traffic surface is supported at the machine frame.
Near the front end sides of the milling roller, height-adjustable side plates are provided as edge protectors at an outer wall of the road milling machine, which side plates, in operation, rest on the ground or traffic surface at the lateral non-milled edges of the milling track. Behind the milling roller, seen in the traveling direction, a height-adjustable stripping means is provided which, in operation, may be lowered into the milling track formed by the milling roller to strip off milling material remaining in the milling track. Further, the road milling machine has a control means for controlling the milling depth of the milling roller and for controlling the setting of the lifting columns.
It is a problem with known road milling machines that, if the machine frame does not extend parallel to the ground, the stripping means will not rest on the ground with sufficient exactness behind the milling roller to allow for a residue-free stripping process to be performed on the surface under treatment. Further, the problem exists that, if the machine frame is not arranged parallel to the ground, the band shoe surrounding the transport band does not flatly rest thereon, so that material which has been milled off may intrude into the region between the band shoe and the still untreated ground surface, or that the function as a hold-down means is performed insufficiently so that chunks of ground material will warp in front of the milling roller and become adhered under the band shoe. Further, the problem exists that the milling depth can not be controlled accurately enough and that, for this reason, the milling depth has to be measured repeatedly by hand during the milling operation. Especially in cases where a hard traffic surface, e.g. concrete, is milled, the tools are worn heavily so that the milling depth set is corrupted by the decreasing diameter of the cutting circle. For example, the wear of the tools, when milling concrete, can cause a difference in the milling radius of 15 mm after only a few 100 meters, so that the measuring of a displacement of side plates, for example, with respect to the machine frame is not sufficiently accurate. If the milling depth is insufficient, a time-consuming reworking of the milling track has to be carried out. Should the milling track be too deep, more building material has to be applied afterwards in order to achieve the desired ground or traffic surface level.